Titanium primer for a vacuum pump



Nov. 22, 1966 E. c. HURST 3,286,820

TITANIUM PRIMER FOR A VACUUM PUMP Filed Sept. 28, 1962 INVENTOR. Zamo/m! 6'- flafs? BY MJW liter/15y United States Patent O "ice 3,286,820 TITANIUM PRIMER FOR A VACUUM PUMP Edmond C. Hurst, Stoughton, Wis., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Sept. 28, 1962, Ser. No. 227,691 1 Claim. (Cl. 206-.4)

The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

This invention relates to vacuum pumps and :more particularly to primers therefor.

The conventional primer of a vacuum pump such as the Evaporion pump described in US. Patent No. 2,850,225 comprises tungsten and titanium wires which are twisted together. The tungsten acts as a support for the titanium which is evaporated to provide a rapid initial gettering action for the evaporion pump. This type of primer is usable only once or twice before failure due to melting. The rate of evaporation of the titanium is not uniform along the length of the primer hence, hot spots develop in the tungsten wire causing it to melt and the primer to fail.

It is therefore one object of the present invention to provide a primer having a relatively uniform rate of evaporation throughout the length thereof.

It is another object of the present invention to provide a primer having a low susceptibility to hot spots.

It is another object of the present invention to provide a primer having a longer life than the conventional primer.

Other objects will become more apparent as the detailed description proceeds.

In general, the primer of the present invention comprises tantalum wire which is helically wound contiguously around titanium wire so that the interstices of the loops of the helix are as small as possible. The titanium wire is melted until it wets the tantalum and appears through the interstices of the helix thereof by capillary action.

Further understanding of the present invention may best be obtained from consideration of the accompanying drawing wherein is shown the contiguous winding of tantalum wire around titanium wire before heating.

A complete understanding of the structure of the primer may best be obtained from consideration of the method of construction thereof.

As shown in the accompanying drawing, tantalum wire is tightly wound around a titanium wire core 12 in a helix so that each loop thereof is in contact with adjacent loops and the interstices 14 therebetween are as small as possible. The primer is then placed in an evacuable chamber (not shown) and the chamber is evacuated to a pressure of at least 10* mm. of Hg. Current is passed through the tantalum wire 10 and is increased in value until the titanium wire 12 melts, wetting the tantalum wire 10, and appearing through the interstices 14 thereof by capillary action.

The point of melting of the titanium wire 10v is critical since at this time there is a danger of the primer melting completely. However, this point may he further detected 3,286,820 latented Nov. 22, 1966 by a change in heating color of the primer which becomes brighter and uniform throughout the length thereof. At this point, the electrical resistance of the whole primer goes down and the applied current rises sharply in value. Thus, the applied current must be decreased rapidly in value to prevent complete melting of the primer. The vacuum is then removed and the primer is ready for use.

. With the primer constructed as described above, a uniform rate of evaporation of the titanium through the interst-ices of the tantalum helix is obtained throughout the length thereof. This ha been found to substantially reduce the susceptibility of the primer to hot spots being developed therein. To further eliminate the occurrence of hot spots in the primer, it is preferred that the diameter of the tantalum wire be approximately equal to the diameter of the titanium wire core of the primer.

The reduction in susceptibility to hot spots in the primer, coupled with an ability for the present primer to store more titanium than the standard primer, give the present primer a longer usable life than the standard primer. Further, it has 'been found that the present primer is able to pull a vacuum at a far greater speed than the conventional primer. Using 40 mil tantalum wire wound around three 20 mil titanium wires, a primer was constructed which had a usable life of at least twice that of the standard primer and which was able to pull a vacuum at least twice as fast as a standard primer. It is to be understood that tungsten may be substituted in place of tantalum for the teachings of the present invention.

Persons skilled in the art will, of course, readily adapt the teachings of the invention to embodiments far different from that illustrated. Accordingly, the scope of protection afforded the inven-tion should not be limited to the particular embodiment shown in the drawing and described above but shall be determined only in accordance with the appended claim.

What is claimed is:

A vacuum pump primer comprising tantalum wire wound in circular helical loops having an internal diameter approximately equal to the diameter of said tantalum wire, with adjacent loops contiguous and the interstices between said loops as small as possible; and a body of titanium filling the interstices of said loop of the helix and the interior thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,605,087 11/1926 Weller 2060.4 X 2,336,138 12/1943 Van Hoorn et al. 2060.4 X 2,534,643 12/1950 Warner 219 2,960,618 11/1960 Waer 313- X 2,986,326 5/1961 Landfors 313-73 THERON E. CONDON, Primary Examiner.

GEORGE N. WESTBY, LOUIS G. MANCENE,

Examiners.

C. R. CAMPBELL, J. M. CASKIE, Assistant Examiners. 

